Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!apple!agate!ucbvax!JESSICA.STANFORD.EDU!almquist
From: almquist@JESSICA.STANFORD.EDU ("Philip Almquist")
Newsgroups: comp.protocols.tcp-ip
Subject: Re: problem with ftp
Message-ID: <9102120205.AA12117@jessica.stanford.edu>
Date: 12 Feb 91 02:05:49 GMT
References: <19910211212243.8.BARMAR@OCCAM.THINK.COM>
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 34

Barry,
> However, it's reasonably safe to assume that
> most media have an MTU of at least 512.  I can't think of any that
> don't, and I would be surprised if anyone invented a new medium with a
> smaller MTU (the current direction is generally towards larger packet
> sizes).

	SATNET had an MTU of somewhere around 250, if I recall
correctly, but I'm pretty sure it's now defunct.  I also seem to recall
that Van uses a similar MTU over his compressed SLIP dialup line (since
he doesn't preempt an FTP data packet that is being transmitted when a
Telnet packet is queued for transmission, he wants to ensure that the
FTP data packet is short enough that its transmission can be completed
without noticeably delaying the transmission of the Telnet packet).  I
don't know what sorts of MTUs are used for packet radio, but they may be
pretty small for similar reasons.

	ATM networks will also use very small packets, but I guess the
expectation is that they will do Link Layer fragmentation to present the
appearance of a reasonably large MTU to the Network Layer.  In general,
I agree that the trend is for new kinds of networks to have much larger
MTUs.

>> Finally, a minor nit: the standards talk about octets rather than bytes.

> I know that, and I debated using "octet" in my message.  I chose to use
> terminology consistent with the question.  It's rarely necessary to make
> this fine distinction outside standards documents...

	Like I said, it was a minor nit, and I almost omitted it.  You
should probably chalk it up to fond memories of the days when I worked
on computers which have a far more flexible concept of what a "byte" is.

							Philip